Hob



Patented Aug. 4, v1936 PATENT OFFICE HOB Ernest C. Head, Rochester', N. Gleason Works, Rochester,

tion of New York Application March 2l,

' ze claims.

The present invention relates to gears which mesh with axes angularly disposed and nonintersecting and particularly to what is known as hypoid gears or gears whose axes are angularly disposed and offset and in which one member of the pair has teeth on its 'side face.

With the methods heretofore used for producing such gears, there have been definite practical limitations as to the amount of offset obtainable in the pair. Meantime, however, in the automotive field especially, there has been a growing demand for larger offsets in order to permit further lowering of the car bodies.

The present invention has for its primary purpose to provide hypoid gearing in which larger offsets can be obtained even in the ratios commonly used in the automotivev field.

Among other objects, the invention has for its purpose to provide hypoid gearing each of whose members can be manufactured in a simple operation and inexpensively, and in which one member of the pair can be hobbed.

The invention broadly has a three-fold character. It consists first in a new form of gearing which comprises a novel form of worm meshing in offset relation with a novel form of gear; second, in a novel form of hob employed to produce the gear; and third, in the new method whereby the gear is hobbed. TheV present application relates specifically to the hobbing process and to the hob employed therein.

The principal objects of the invention have been described. Other objects of the inventionv will appear hereinafter from the specification and from the recital of the appended claims.

In the drawings:

Figure 1 is a side elevation of a pair of gears produced according to this invention;

Figures 2 and 3 are a plan view anda side elevation, respectively, illustrating the preferred method of hobbing the gear or larger member of the pair; and

Figure 4 is a sectional view which may be considered a section in an axial plane through either a taper worm or a taper hob constructed according to this invention.

It has heretofore been suggested (see the Trbojevich Patent No. 1,647,157 of November 1,

1927) that hypoid gearing might be produced by using a worm as the pinion or driver and by cutting the gear with a hob which is a counterpart of the worm and which during cutting is positioned and maintained in the same offset and angular relation to the gear blank as the worm itself. occupies when in mesh with the finished Y., assigner to N. Y., a corpora- 1931, serial No. 524,329 (ci. zia- 103) gear. This method has the advantage o1' simplicity because the worm can be produced in an ordinary lathe and the gear can be hobbed without a generating roll, but such hypoid gearing up to the present has not come into use commercially. 5 The principal disadvantage has been that it has heretofore been conned to use in large reductions for, up to the present, it has not been practical to make pairs employing other than a singlethread worm.

My invention constitutes an improvement on the type of gearing described in the Trbojevich patent above mentioned in that it permits of using a multiple-thread worm as one member of the hypoid pair, the number of threads in the worm 15 being determined by the ratio desired. The method of cutting the gear is of the same general character described in the Trbojevich patent, the gear being cut with a hob, which is a counterpart of the worm or' generally so, by rotating the hob 20 and gear blank together in timed relation and imparting a simple depthwise feed motion to cut 'teeth-of proper depth on the gearblank, but the worm and hob and, therefore, the gear are different in construction from the worm, hob and 25 gear illustrated in the Trbojevich patent.

Heretofore, when a multiple-thread taper worm or hob has been used to cut a tapered gear, the teeth cut in the gear have had pressure angles changing from their outerr to their inner ends to so extreme a degree as to render the gear impractical for use. In my improved gearing, however, instead of using a worm of uniform pressure angle from one end to the other, as is the usual practise and as is described in the Trbojevich patent, I modify the pressure angles of the threads of the worm and of the corresponding hob from one end to the other and to such an extent that a practical form of gear tooth is obtained, a tooth either of uniform pressure angle from end to end or one 10 varying in pressure angle within narrow and unobjectionable limits.

As the pressure angles of teeth of a tapered gear cut with a multiple-thread hob of uniform pressure angle areexcessive at the outer or large ends of the teeth and too small at the inner or small ends of the teeth, I make the threads of my hob and worm so that the pressure angle is greatest at the small end of the hob, the end which cuts the inner end: of the teeth of. the gear, and least at the large end of' the hob, the end which cuts the outer ends of the teeth of the gear. Incidentally this structure gives added strength to worm and hob for the increased pressure angle of the threads at the small end of the 55 hob and worm give increased strength where it is most needed. As it is desirable to cut both bevel and hypoid gears with teeth tapering in depth from their outer to their inner ends, the teeth of my hob and the threads of my worm are tapered in height from the large to the small end of the hob and worm. Now with this construction, if the hob thread were of the same lead on opposite sides, the teeth at the small end would be of disproportionate width at their tips or lands and would accordingly cut the inner ends of the tooth spaces of the gear disproportionately wide. To avoid this condition, I have found it desirable to form the threads of both hob and worm of different lead on opposite sides. For the sake of simplicity in manufacture and the greater ease in calculating gears and hobs, both sides of the threads are, however, made of uniform lead. If gears having teethoi parallel depth, that is, of uniform height from end to end, were to be cut, the threads of hob and worm would not have to be tapered in height .and the tips or lands of the threads could be made of uniform width from end to end of hob and worm by changing the pressure angle alone.

Referring to the drawings by numerals of referce, I0 denotes the gear and II the worm or pinion of a pair of hypoid gears constructed according to the present invention. The axis I2 of the worm is oifset from the axis I3 of the gear a distance X. The worm is tapered and is provided with a plurality of threads or teeth I4 which are curved longitudinally about the axis of the worm and which mesh with the correspondingly curved teeth I5 of the gear. The teeth of the gear are cut conjugate to the threads of the worm. The number of teeth in worm and gear are determined by the reduction desired.

Figure 4 shows in axial section, the preferred construction of the worm. It has threads I4 whose sides I6 and I'I are of changing pressure angle from end to end. Thus, the pressure angle of the sides I'I of the threads I4 increases from right to left, the pressure angle at a being larger than at al which in turn is larger than at a2 and so on, the pressure angle for the sides II, in the section shown, being at a' minimum at a4 and at a maximum at a. Likewise, on the other side I6 of the thread, the pressure angles vary from b to b4, being at a maximum in the section shown, at b and a minimum at b4. The change in pressure angle from end to end on the two sides of the worm threads is such as to permit of making the teeth I5 of the gear of approximately uniform pressure angle from end to end. It will be noted that the pressure angles of opposite sides of the worm thread are largest at the small end of the worm. This gives added strength where it is most needed.

The worm is preferably made with teeth tapering in height from its large end to its small end as shown and the gear has teeth tapering correspondingly in height from their outer to their inner ends.

For the purpose of simplicity in manufacture both of the worm and of the corresponding hob for cutting the gear, and also because of the desirable tooth shapes obtainable on the gear, the threads of the worm are turned so that their sides I6 and I1 are straight in axial section as shown. Likewise, because of the manifest advantages in manufacture and the greater ease in calculating the gears, I prefer to make the sides of the worm threads of uniform pitch in axial section, but to avoid excessive width of the threads at their small ends with a corresponding excessive widthof the tooth spaces of the gear I5 at their small ends, which would result if the threads of the worm were tapered in height 5 Without any other change, the threads of the worm are made of different pitch on opposite sides.

20 denotes the pitch surface of the worm when running in mesh with its mate gear I0. 2| denotes the top surface of the worm and 22 its root surface. 24 denotes a line parallel to the root surface of the worm. For Convenience in manufacture, as will hereinafter appear, I prefer to make the sides I6 and I1 of the threads of the worm of uniform pitch along this line. The pitch of the sides I6 of the thread I4 is indicated at P. The pitch of the sides II of the threads is indicated at P'. The two pitches P and P are each uniform along the line 24, but 20 they are diierent.

The gear will have teeth I5 whose sides are correspondingly of uniform pitch along a line coinciding with the projection of the worm axis, the pitch being different on the two sides of the 25 teeth corresponding to the difference in pitch of opposite sides of the worm threads.

The gear I0 of the pair is cut with a hob H which is preferably made a counterpart of the worm II. It is formed with a plurality of threads 30 which are gashed at 25 and relieved to form cutting teeth 26. If an exact counterpart of the Worm, the number of threads in the hob will be the same as the number of threads in the worm II and like the threads I4 of the worm II, the 35 pressure angle of the sides of the thread of the hob will change from one end of the hob to theother and in the same respect and to the same extent as the pressure angle of the threads of the worm. The leads of the hob threads will be different on opposite: sides of the thread, the pitches of opposite sides of the hob threads will be different and equal, respectively, to the pitches p and p of opposite sides of the Worm threads. The pitches of the sides of the hob threads will be uniform along a line corresponding to the line 24 and parallel to the root line 22 of the hob. This construction permits of readily relieving the hob on a lathe such as described in my pending application No. 447,011 of April 24, 1930. The teeth of the hob will taper in height from the large end to the small end thereof and preferably to the same extent as to the teeth of the worm. As stated with reference to the worm, the increased pressure angle of the teeth at the small end of the hob gives increased strength. The sides of the hob will be straight in axial section as shown in Figure 4. This permits of relieving the hob with a straight-sided lathe tool placed on center and gives a more desirable tooth structure in the gear and in the corresponding worm. Figure 4 may be considered an axial section either through the worm I I or the hob H.

The worm can be cut upon a machine similar to that described in my pending application No. 65 447,011 by omitting the relieving attachment and simply using the machine as a worm-cutting lathe.

The gear I 0 is cut by positioning the hob H with its axis 28 offset from the axis I3 of the 70 gear blank the same distance X as the worm II is offset when in mesh with the gear and the hob is preferably positioned, also, with reference to the gear blank so that its axis 28 is inclined to the axis I3 of the gear blank at the same angle 75 as that to which the worm II is inclined to the axis I3 of the gear I0 when the two are inl mesh. In the drawings, this angle is 90. The offset between the cone apex 29 of the hob H and the cone apex 30 of the gear blank I0 is preferably the same as the offset between the cone apex of the worm and the cone apex 30 of the gear when the worm and gear are in mesh. If the apex of the worm when in mesh with the gear lies on the line X perpendicular to the axes I3 and I2, respectively, of the gear and worm, the offset is,

of course, zero. The pitch cone angle 3| of the hob is preferably the same as the pitch cone angle of the worm Il.

To cut the gear, the hob H is positioned as described, and the hob and gear blanks are rotated continuously on their axes 28 and I3, respectively, in timed relation while a depthwise feed is produced between the hob and blank to cause teeth of proper depth to be cut in the blank. During this fed motion, the angular and offset relations of the hob and blank axes are maintained constant so that when the hob has reached full depth position, its teeth will sweep out the whole of the finished tooth surfaces of the gear I0. There is no generating roll employed. The gear may be cut upon a machine of the type described in the Trbojevich patent above mentioned.

I have stated above that preferably the hob is made a counterpart of the worm II. However, the dimensions of the hob or its position in cutting the gear may be slightly different from the dimension of the worm or the position of the worm when it meshes with the gear, for the purpose of obtaining a localization of tooth bearing between the worm and gear, as will be readily understood by those skilled in the art.

While the invention has been described in connection with the production of a pair comprising a tapered gear and worm, it will be understood that the principles of the invention apply broadly, also, to such hypoid pairs as include a cylindrical worm and a conjugate mating crown gear. In general it may be said that while I have described particular embodiments of my invention, it will be understood that the invention is capable of various further modifications and uses and that this application is intended to cover any adaptations, uses, or embodiments of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the gear art and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. A hob formed by gashing and relieving a thread to form a series of finishing teeth which together generate the final finished shape of the work, said thread being of different lead on opposite sides but of uniform lead on each side and being of straight profile in an axial plane.

2. A taper hob formed by gashing and relieving a thread to form a series of finishing teeth which together generate the final finished shape;

of the work, said thread being of different lead on opposite sides but of uniform lead on each side and being of straight profile in an axial plane.

3. A taper hob formed by gashing and relieving a thread to form a series of nishing teeth which together generate the final finished shape of the work, said thread along a line parallel to its root line being of different lead on opposite sides but of imiform lead on each.

4. A taper hob formed by gashing and relieving a thread to form a series of finishing teeth which together generate the final finished shape of the work, said thread on each side being of changing pressure angle `from one end to the other and of different lead on its opposite sides.

5. A taper hob formed by gashing and relieving a thread to form a series of finishing teeth which together generate the final finished shape of the work. said thread on each side being of changing pressure angle from one end to the other and being of different lead on its opposite sides but of uniform lead on each side.

6. A taper hob formed by gashing and relieving a thread t form a series of finishing teeth which together generate the final finished shape of the work, said thread on each side being of changing pressure angle from one end to the other and being of different lead on opposite sides but of uniform lead on each along a line parallel to its root line. y

7. A taper hob formed by gashing and relieving a multiple-thread Worm to form a series of finishing teeth which together generate the final finished shape of the work, the threads of said Worm being of increasing pressure angle on each side from the large to the small end of the hob and of different lead on their opposite sides.

-8. A taper hob formed by gashing and relieving a multiple-thread taper worm to form a series offinishing teeth which together generate the final finished shape of the work, the threads of said worm being of increasing pressure angle on each side from the large to the small end of the hob and of different lead on opposite sides, -but of uniform lead on each side.

9. A taper hob formed by gashing and relieving a multiple-thread worm to form a series of finishing teeth which together generate the final finished shape of the work, the threads of said Worm being of increasing pressure angle from the large end to the small end of the worm and of uniform lead on one side measured along a line parallel to the root line of the worm.

10. A hob formed by gashing a thread toA form a series of finishing teeth which together generate the final finished shape of the work, said thread being of constant axial pitch on one side face thereof and of a different constant axial'pitch on the other side face thereof. r

11. A taper hob formed by gashing a thread to form a series of finishing teeth which together generate the final finished shape of the work, said thread being of constant axial pitch on one side face thereof and of a different constant'axlal pitch on the other side 'face thereof.

12. A generating hob having a helical thread of a constant mean lead and consisting of a series of successive finishing teeth, said thread in one direction ltapering uniformly both in width at the pitch line and in height, the sides of said thread having different leads.

13. A generating hob having a helical thread consisting ofa series of successive finishing teeth thereon, said teeth having different constant axial pitches on the oppositeproiile generating faces thereof, and said teeth being of uniformly varying width at the pitch line.

14. A multiple-thread hob whose threads are each of different lead on opposite sides and are each gashed and relieved to forma series of finishing teeth which together generate the finished surface of the work.

15. A multiple thread hob whose threads are each of different but uniform lead on opposite sides and are each gashed and relieved to form a series of finishing teeth which together generate the finished surface of the work.

16. A multiple thread hob whose threads are each of straight profile in axial section but of different lead on opposite sides and are each gashed and relieved to form a series of nishing teeth which together generate the finished surface of the work.

17. A multiple .thread hob whose threads are each of straight profile in axial section and of different but uniform lead on opposite sides and are each gashed and relieved to form a series of finishing teeth which together generate the nished surface of the work.

18. A multiple thread hob Whose threads are of different lead on opposite sides and are gashed and relieved to provide a series of finishing teeth which increase in height from one end of the hob to the other and which together generate the nished surface of the work.

19. A multiple thread hob Whose threads are of different but uniform lead on opposite sides and are gashed and relieved to provide a series of nishing teeth which increase in height from one end of the hob to the other and which together generate the finished surface of the work.

20. A multiple thread hob whose threads are of straight profile in axial section and of different lead on opposite sides and gashed and relieved to provide a series of finishing teeth which increase in height from one end of the hob to the other and which together generate the finished surface of the Work.

21. A multiple thread hob whose threads are of a,oso,ass

dilferent but uniform lead on opposite sides and of straight profile in axial section and gashed and relieved to provide a series of nishing teeth which increase in height from one end of the hob to the other and which together generate the nished surface of the work.

22. A multiple thread hob whose threads are each of diierent lead on opposite sides and of continuously changing pressure angle from one end of the hob to the other and whose threads are each gashed and relieved to form a series of finising teeth which together generate the finished surface of the work.

23. A multiple thread hob whose threads are each of different but uniform lead on opposite sides and of continuously changing pressure angle from one end of the hob to the other and whose threads are each gashed and relieved to form a series of finishing teeth which together generate the finished surface of the work.

24. A multiple thread hob Whose threads are each of straight profile in axial section but of diferent lead on opposite sides and of continuously changing pressure angle from one end of the hob to the other and whose threads are gashed and 25 

